Fix bug handling errors in subscribePlan execution

.changeset/violet-planets-bow.md

@@ -0,0 +1,6 @@
+---
+"grafast": patch
+---
+
+Fix bug handling an error raised in subscribePlan execution that was resulting
+in websocket closure.

grafast/grafast/src/prepare.ts

@@ -427,12 +427,12 @@ function executePreemptive(
       // Something major went wrong!
       const errors = [
         new GraphQLError(
-          bucketRootValue.originalError.message,
+          bucketRootValue.message,
           operationPlan.rootOutputPlan.locationDetails.node, // node
           undefined, // source
           null, // positions
           null, // path
-          bucketRootValue.originalError, // originalError
+          bucketRootValue, // originalError
           null, // extensions
         ),
       ];

postgraphile/postgraphile/graphile.config.ts

@@ -384,6 +384,28 @@ const preset: GraphileConfig.Preset = {
         },
       },
     }),
+    makeExtendSchemaPlugin({
+      typeDefs: gql`
+        extend type Subscription {
+          error: Int
+        }
+      `,
+      plans: {
+        Subscription: {
+          error: {
+            subscribePlan: EXPORTABLE(
+              (constant, lambda) =>
+                function subscribePlan() {
+                  return lambda(constant(3), () => {
+                    throw new Error("Testing error");
+                  });
+                },
+              [constant, lambda],
+            ),
+          },
+        },
+      },
+    }),
     // PrimaryKeyMutationsOnlyPlugin,
     PersistedPlugin,
     makeRuruTitlePlugin("<New title text here!>"),